1. Field of the Invention
The present invention relates to a composition for forming a titanium-containing resist underlayer film used in a multilayer resist film used in fine processing in a process for producing a semiconductor device and so on, and a patterning process using the same.
2. Description of the Related Art
In the 1980s, exposure light whose source is g-beam (436 nm) or i-beam (365 nm) of a mercury lamp was commonly used for resist patterning. To achieve a further micro resist pattern, a method for making exposure wavelength shorter has been regarded as more effective means. In the 1990s, 64 MB (work size: 0.25 μM or less) dynamic random access memory (DRAM) and subsequent electronic devices were mass produced, in which short-wavelength KrF excimer laser (248 nm) were employed as an exposure source instead of the i-beam (365 nm). In reality, however, the production of DRAMs with an integration degree of 256 MB and 1 GB or more requires finer processing technology (work size: 0.2 μM or less), and needs a light source of shorter wavelength. Amid this technological need, the introduction of photolithography using ArF excimer laser (193 nm) has been seriously studied since about a decade ago. According to initial strategy, ArF lithography was going to be introduced in conjunction with the production of 180 nm-node devices, but a conventional KrF excimer lithography was continuously used until 130 nm-node device mass production. Therefore, official introduction of ArF lithography started with 90 nm-node device production. Meanwhile, mass production of 65 nm-node devices, having lenses whose numerical aperture (NA) was raised to 0.9, are being promoted. Because of advantageous shorter exposure wavelength, F2 lithography with wavelength of 157 nm was regarded as a next promising production technology for subsequent 45 nm-node devices. However, development of F2 lithography was canceled due to several problems such as higher scanner costs from expensive CaF2 single crystals into projection lenses in large volumes, change in the optical system in accordance with introduction of hard pellicles instead of conventional extremely low durable soft pellicles, and reduced etch resistance of a resist film, thereby introducing ArF-immersion lithography. In the ArF-immersion lithography, water with a refractive index of 1.44 is inserted between a projection lens and a wafer by partial fill method, enabling high-speed scanning. Accordingly, 45 nm-node devices are mass produced by using lenses with an NA of 1.3.
Extreme-ultraviolet (EUV) lithography with wavelength of 13.5 nm is regarded as a next promising fine processing technology by using 32 nm-node lithography. Unfortunately, the EUV lithography is prone to numerous technical problems such as needs for higher laser output, higher sensitivity of a resist film, higher resolution, lower line edge roughness (LER), use of defect-free MoSi laminated mask, and lower aberration of a reflective mirror. Development of another promising 32 nm-node device production technology, or high-refractive index immersion lithography, was canceled due to low transmission factor of another promising high-refractive index lens (LUAG) and an inability to obtain a target value of liquid's refractive index at 1.8. Under the circumstances, general-purpose light exposure technology seems to fail to significantly improve the resolution unless light source wavelength is changed.
Accordingly, development of a fine processing technology for obtaining a work size exceeding a limiting resolution of an existing ArF-immersion exposure technology has been promoted. As a technology thereof, double patterning technology is being proposed. Specifically, the double patterning technology is a method (method (1)) for forming a first photoresist pattern with an interval rate of a line to a space of 1:3 by using first exposure and development, processing an underlayer hard mask by dry etching, laying another hard mask thereon, forming a second line pattern at a space portion obtained by the first exposure by using second exposure and development of a photoresist film, processing the hard mask by dry etching, and alternately forming the first pattern and the second pattern. By this method, it is possible that forming a pattern whose pitch is half that of an exposure pattern. Also, there is another method (method (2)) for forming a first photoresist pattern with an interval rate of a line to a space of 1:3 by using first exposure and development, processing an underlayer hard mask, forming a pattern on a remaining portion of the hard mask by using second exposure by applying a photoresist film on the underlayer hard mask, and processing the hard mask by dry etching with the pattern as a mask. In both methods, by processing a hard mask by two dry etching, a pattern whose pitch is half that of an exposure pattern can be formed. Nevertheless, while the method (1) requires formation of a hard mask twice, the method (2) needs one-time hard mask formation, but additional formation of a trench pattern which is more difficult to resolve than a line pattern.
Another method (method (3)) proposed is to form a line pattern on a positive resist film in X direction by using a dipole light, cure a resist pattern, apply a resist composition thereon again, expose a line pattern in Y direction by using a dipole light, and form a hole pattern from a gap of a grid-like line pattern (Non-Patent Document 1). Moreover, with a resist pattern, an organic hard mask whose pattern is transferred and a polysilicon film as a core pattern, a method for halving a pitch by one-time pattern exposure by spacer technology of removing a core pattern by using dry etching, after forming a silicon oxide film therearound at a low temperature, is being proposed.
Accordingly, since finer processing is difficult to achieve only by using a resist film present in an upper layer, a micropatterning process cannot readily be introduced without using a hard mask formed in an underlayer of a resist film. Under the circumstances, multilayer resist method is known as a method for using a hard mask as a resist underlayer film. The method is to transfer a pattern in a resist underlayer film by dry etching, with an upper layer resist pattern as an etching mask, after interposing a photoresist film, or a middle layer film whose etching selectivity is different from a resist upper layer film (e.g. a silicon-containing resist underlayer film) between a resist upper layer film and a substrate to be processed to obtain a pattern in the resist upper layer film, and further transfer a pattern on the substrate to be processed or a core film for processing a spacer by dry etching, with a resist underlayer film as an etching mask.
Illustrative example of the composition for forming a resist underlayer film used in this multilayer resist method includes a silicon-containing inorganic film obtained by CVD method such as an SiO2 film (e.g., Patent Document 1) and an SiON film (e.g., Patent Document 2), and illustrative example of a spin-coating film includes a spin-on glass (SOG) film (e.g., Patent Document 3) and a crosslinking silsesquioxane film (e.g., Patent Document 4).
Also, conventional researches have focused on advantages of a resist underlayer film that can be used in multilayer resist method to provide a composition for forming a silicon-containing resist underlayer film disclosed in Patent Documents 5 and 6. Nevertheless, in a process for producing a semiconductor device whose resolution of a recent ArF-immersion lithography exceeds a limiting resolution thereof, complex processes such as the above described double patterning are being proposed, and it is increasingly difficult to construct a reasonable process for finer processing technology only by using conventional types of organic films and silicon-containing films. Accordingly, in order to construct a more reasonable process for producing a semiconductor device, introduction of a coating film containing a component having etching selectivity relative to an organic film and a silicon-containing film that are currently and widely applied and having pattern adhesiveness relative to a finer pattern.
Under the circumstances, a resist underlayer film containing various metal species is proposed as a coating film having etching selectivity relative to organic film and silicon-containing film (Patent Documents 7 to 9). For instance, Patent Document 7 discloses KrF exposure patterning evaluation using polytitanoxane, but no patterning evaluation using ArF-immersion exposure is described therein. With no patterning evaluation, Patent Document 8 doesn't describe whether actual patterning performance is verified or not. Patent Document 9 proposes introduction of not only titanium- but also zirconium-containing resist underlayer films, but this technology is free from patterning evaluation, thereby making the actual performance unproved. Accordingly, it is unidentified whether these coating films have an adhesive property relative to a finer pattern or not.
In addition, a coating film containing a titanium alkoxide is proposed as the one having the above characteristics. In fact, it is generally known that a titanium alkoxide, if subjected to hydrolysis and condensation, shows higher reactivity to water than a silicon alkoxide (Patent Document 10 and Non-Patent Document 2). Unfortunately, this property leads to changes in characteristics of a coating film when this type of coating film is connected to an apparatus for producing a semiconductor device in a process for producing the same, resulting in fatal defects in the use.
Accordingly, new technologies require a coating film having favorable etching selectivity relative to conventional organic film and silicon-containing film, favorable pattern adhesiveness relative to a fine pattern, and sufficient storage stability that shows no changes in characteristics as a coating film even when it is connected to an apparatus for producing a semiconductor device.